摘要:

AbstractA series of dilute liquid crystalline solvents are used to study the effect of slight anisotropy caused by partial alignment on chemical shift and residual dipolar coupling (RDC) in small molecules. The residual dipolar couplings between protons in solutes are found to be almost independent of the local environment. It is also found that the chemical shift does not change over the concentration range observed. A linear relationship between residual dipolar coupling and liquid crystal concentration is observed at relatively low concentrations, but is severely violated at high concentrations.

ISSN:0009-4536    

DOI:10.1002/jccs.200500001

出版商:WILEY‐VCH Verlag    

年代:2005

数据来源: WILEY

摘要:

AbstractDielectric relaxation measurements on aqueous solutions of alanine and phenylalanine were carried out using time domain reflectometry (TDR) at 25, 30, 35, and 40 °C in the frequency range from 10 MHz to 20 GHz. Aqueous solutions of alanine and phenylalanine are prepared for five different molar concentrations of the respective amino acid. For all the solutions considered, only one relaxation peak was observed in this frequency range. The relaxation peaks shift to lower frequency with an increase in alanine and phenylalanine molar concentration. The molar enthalpy of activation and molar entropy of activation show endothermic interactions

ISSN:0009-4536    

DOI:10.1002/jccs.200500002

出版商:WILEY‐VCH Verlag    

年代:2005

数据来源: WILEY

摘要:

AbstractA linear solvation free energy relationship has been conducted to study the effects of solvent and solute properties on the free energy of solvation of inert gases and normal alkanes in different solvents. Factor analysis combined with target factor analysis was used to identify and quantify the factors controlling the variation of free energies of solvation, without the need to postulate any priori hypothetical method. Factor analysis of the solvation data revealed that there are two factors affecting the solubility of both types of gases in non‐polar as well as polar solvents. Target testing of the solvent parameters indicated that the Hildebrand solubility parameter of solvents is the major factor controlling the solubility of gases. Moreover, it was found that the coefficient of the Hildebrand solubility parameter in the linear solvation free energy equations has linear correlation with energy of vaporization and Lennard‐Jones force parameter of inert gases and number of carbon atoms and energy of vaporization of normal alka

ISSN:0009-4536    

DOI:10.1002/jccs.200500003

出版商:WILEY‐VCH Verlag    

年代:2005

数据来源: WILEY

摘要:

AbstractDifferential Pulse Voltammetry has been used for the simultaneous determination of cysteine, tyrosine and trptophan on the unmodified glassy carbon electrode. In the analysis of these analytes in the same samples, the main difficulty is the high degree of overlapping of voltammograms. The relationships between the currents and the concentrations are complex and highly nonlinear. The predictive ability of principal component regression (PCR), partial least squares regression (PLS), genetic algorithm‐partial least squares regression (GA‐PLS) and principal component‐artificial neural networks (PC‐ANNs) were examined for simultaneous determination of three amino acids. For a regression model, everything that could not help in constructing the model may be considered as noise without further specification. PC‐ANN and GA‐PLS use significant data and show superiority over other applied multivariate methods. The proposed method was also applied satisfactorily to determination of analytes in some synthe

ISSN:0009-4536    

DOI:10.1002/jccs.200500004

出版商:WILEY‐VCH Verlag    

年代:2005

数据来源: WILEY

摘要:

AbstractThe present paper presents a study on the anode dissolution and corrosion of aluminum electrodes by electrolysis of aqueous solutions of sodium chloride in a magnetic field. The electrolysis was carried out under a galvanostatic regime with direct current and a uniform electric field. The magnetic field was generated by permanent magnets placed along the axis between an anode and cathode. The parameter current efficiency was used as a measure of the non‐conformity with the generalized Faraday law observe

ISSN:0009-4536    

DOI:10.1002/jccs.200500005

出版商:WILEY‐VCH Verlag    

年代:2005

数据来源: WILEY

摘要:

AbstractThe adsorption of Chromium(VI) from aqueous solutions was studied on different commercial grades of granular activated carbon namely Filtrasorb F‐400, F‐300, F‐200 and F‐100. The adsorption of Chromium (VI) on F‐400 carbon was found to be maximum in comparison to the other grades of carbon. The Chromium (VI) adsorption process in dilute aqueous solutions agreed with the Langmuir and Freundlich models and also obeyed first order kinetics. Metal sorption characteristics of as received activated carbons were measured in batch experiments. The maximum removal (60–65%) for different grades of raw carbon was observed at 25 °C with an initial concentration of 15.16 mg dm−3. It is evident from the study that granular activated carbon holds a particular promise in the removal of metal ions from aqu

ISSN:0009-4536    

DOI:10.1002/jccs.200500006

出版商:WILEY‐VCH Verlag    

年代:2005

数据来源: WILEY

摘要:

AbstractDecylammonium tetrachlorozincate (n‐C10H21NH3)2ZnCl4(C10ZnCl), dodecylammonium tetrachlorozincate (n‐C12H25NH3)2ZnCl4(C12ZnCl) and hexadecylammonium tetrachlorozincate (n‐C16H33NH3)2ZnCl4‐(C16ZnCl) were synthesized and a series of their mixtures C10ZnCl‐C16ZnCl and C12ZnCl‐C16ZnCl were prepared. The experimental binary phase diagrams of C10ZnCl‐C16ZnCl and C12ZnCl‐C16ZnCl were established by means of differential scanning calorimetry (DSC), IR and X‐ray diffraction. In the phase diagram a stable solid compound and two eutectoid invariants were observed. It is noticeable that the phase diagram contains soli

ISSN:0009-4536    

DOI:10.1002/jccs.200500007

出版商:WILEY‐VCH Verlag    

年代:2005

数据来源: WILEY

摘要:

AbstractA sensitive reagent system is proposed for the determination of cyanide and hydrogen cyanide in various environmental samples. The method is based on the conversion of cyanide into cyanogen bromide followed by its reaction with pyridine to form glutaconic aldehyde. The glutaconic aldehyde so formed is coupled with p‐aminoacetophenone forming yellow‐orange polymethine dye measured at 445 nm. The colour system obeys Beer's law in the range of 0.01–0.16 ppm of cyanide inaqeous phase and 0.002–0.03 ppm in extracting system. The molar absorptivity and Sandell's sensitivity were found to be 6.51 × 105l mol−1cm−1and 0.0001 μg cm−2, respectively. The method has been successfully applied for the determination of cyanide in air, industrial effluent, biological samples, and in the pesticid

ISSN:0009-4536    

DOI:10.1002/jccs.200500008

出版商:WILEY‐VCH Verlag    

年代:2005

数据来源: WILEY

摘要:

AbstractThe investigations of the ultrasonic decomposition of NH3‐N and organic compounds (i.e., CODCr) in coke plant wastewater are presented in this work. The process parameters were controlled with respect to the presence (or absence) of air atmosphere, initial pH value, initial concentration, and ultrasonic power density in the process of ultrasonic decomposition. It is noted that the ultrasonic removal efficiencies for both the NH3‐N and the CODCrwere increased in the presence of the air atmosphere and significantly affected by the initial pH value. The removal efficiencies increased with increasing the ultrasonic power density while they decreased with increasing the initial concentration. The effects of n‐butyl alcohol as an effective OH radical scavenger on the removal efficiencies indicates that the ultrasonic decomposition of the NH3‐N was carried out mainly via the mechanism of thermal decomposition in cavitation bubbles or in the interfacial region, whereas the ultrasonic decomposition of the CODCrmainly resulted from the reactions with OH radicals in the bulk solution. The GC/MS analysis indicates that most of the organic compounds in the wastewater were effectively destroyed by ult

ISSN:0009-4536    

DOI:10.1002/jccs.200500009

出版商:WILEY‐VCH Verlag    

年代:2005

数据来源: WILEY

摘要:

AbstractA novel kinetic method for the determination of trace amounts of Co(II) has been developed. The proposed method based on the catalytic effect of Co(II) on the oxidation of xylenol orange tetra sodium salt by H2O2in the presence of cationic surfactant (N‐dodecylpyridinium chloride). Co(II) at μg.mL−1was determined spectrophotometrically by measuring the decrease in the absorbance of xylenol orange at 577 nm by the differential method. The method is precise, selective, and sensitive. The detection limit of the procedure was 0.058 μg.mL−1. The relative standard deviation for the replicate determination (n = 6) of 0.7 μg.mL−1was 1.285%. The results compared satisfactorily with those of atomic absorption spectrometry. The method was successful for the analysis of Co(II) in veterinary and synthet

ISSN:0009-4536    

DOI:10.1002/jccs.200500010

出版商:WILEY‐VCH Verlag    

年代:2005

数据来源: WILEY